1. Field of the Invention
This invention relates to an electrophotographic apparatus, and in particular to an electrophotographic apparatus which is capable of changing the copying magnifications in a one-dimensional direction and a two-dimensional direction.
2. Description of the Prior Art
In electrophotographic apparatuses such as copying apparatuses, the imaging lens system for imaging an original on a light-receiving member such as a photosensitive drum has heretofore been comprised of a magnification changing lens system to vary the copying magnification of the original.
FIGS. 1A-1C of the accompanying drawings show a basic two-dimensional direction magnification changing method in the electrophotographic apparatus according to the prior art. In these Figures, reference numeral 1 designates an original which is the object surface, reference numeral 2 denotes a light-receiving member which is the image plane, reference numeral 3 designates an imaging lens system, reference numerals 31, 32, 33 and 34 denote constituent lenses, and reference numeral 4 designates a stop. FIG. 1A shows the case of reduction (when the imaging magnification is .beta., .vertline..beta..vertline.&lt;1), FIG. 1B shows the case of one-to-one magnification, and FIG. 1C shows the case of enlargement.
Usually, the imaging magnification in the apparatus of this type is used about one-to-one magnification and therefore, the imaging lens system 3 has a symmetrical shape with respect to the stop 4 as shown, and the whole of the imaging lens system 3 is moved in the direction of the optic axis thereof to effect a magnification change and the lenses 31 and 34 in the imaging lens system 3 are moved by the same distance in opposite directions, thereby correcting any variation in the position of the image plane resulting from the magnification change.
In an electrophotographic apparatus like the above-described example of the prior art, the lenses 31 and 34 become spaced apart from the stop 4 during a magnification change and therefore, the apertures of the lenses must be made great and wider angles of views of the lenses have hindered compactness of the entire optical system. There is also a method in which the lenses 31 and 34 are fixed and the lenses 32 and 33 are moved, but again in this case, the space for movement of the lenses 32 and 33 becomes necessary and therefore, a problem similar to that described above arises. Also, the individual lenses must be moved with the movement of the entire imaging lens system, and this has led to the complication of the lens barrel and the complication of the driving mechanism, which in turn has led to a problem in terms of cost.
There is also known an apparatus in which, in addition to thus varying the copying magnification in the two-dimensional direction, the copying magnification only in the one-dimensional direction of the original can be varied. The electrophotographic apparatus of this type, as compared with the above-described electrophotographic apparatus in which the size of the image can be two-dimensionally varied, has an advantage that additional information can be printed in a continuous form on the blank space portion of the copy image.
FIGS. 2A-2C of the accompanying drawings illustrates the copy image in a case where the original has been two-dimensionally reduced and the copy image in a case where only one direction of the original has been reduced. In the copy image B wherein the original A has been two-dimensionally reduced, an L-shaped blank space portion is created and therefore, if the same form is adopted when additional information X is printed, a blank is created. However, in the copy image C wherein the original has been reduced only in one direction (the lengthwise direction), a blank space portion is only created in the upper or lower portion of the paper and the additional information X can be printed without the form being altered. The function of changing the magnification only in one direction of an original has an additional advantage that even if characters are reduced in order not to vary the information density in one direction, the characters are easy to read.
FIG. 3 of the accompanying drawings illustrates the structural principle of an electrophotographic apparatus according to the prior art which is capable of varying the magnification only in one direction.
In FIG. 3, reference numeral 5 designates an original carriage, reference numeral 6 denotes an original, reference numeral 7 designates an illuminating optical system, reference numeral 8 denotes a slit, reference numeral 12 designates a photosensitive drum, reference numeral 14 denotes a cylinder lens, arrows indicate the directions of movement of the original carriage 5 and the photosensitive drum 12, and m and M represent the movement velocities of the original carriage 5 and the photosensitive drum 12, respectively. As shown, the original 6 placed on the original carriage 5 is illuminated by the illuminating optical system 7, and the illuminated image passes through the slit 8 and is imaged and recorded on the light-receiving member 12 such as a photosensitive drum by a rotation-symmetrical imaging lens system 3. The movement velocity m of the original carriage 5 and the angular velocity M of the light-receiving member 12 are suitably set in accordance with the imaging magnification.
Where reduction is to be effected with respect to one direction (in FIG. 3, x direction) of the original 6 and imaging and recording at one-to-one magnification is to be effected with respect to y direction, the ratio between the velocity m and the angular velocity M is varied in conformity with the reduction rate. However, if, at this time, the imaging lens system remains at one-to-one magnification, the image recorded on the light-receiving member 12 will be blurred with respect to the x direction and therefore, it s necessary to correct the imaging magnification with respect to the x direction. Thus, in the electrophotographic apparatus according to the prior art, the cylinder lens 14 for correcting the magnification has been inserted just in front of the imaging plane of the light-receiving member 12, and the imaging magnification in the x direction has been made coincident with the reduction rate, thereby correcting the imaging magnification. The cylinder lens 14 has a bus line in a direction perpendicular to the plane of the drawing sheet, and its length corresponds to the length of the light-receiving member 12 in the direction perpendicular to the plane of the drawing sheet. Accordingly, as described above, in the electrophotographic apparatus according to the prior art, the operation of inserting the cylinder lens 14 into the optical path to change the magnification in one direction of the original 6 has been necessary, and this has led to a disadvantage that the length of the optical path between the original 6 and the light-receiving member 12 is greatly fluctuated by inserting the cylinder lens 14 and a clear image cannot be obtained.
Also, to provide a plurality of reduction or enlargement magnifications in one direction of the original, it is necessary to prepare plural types of cylinder lenses, and this has led to a disadvantage that a wide space is required within the apparatus and the mechanical construction of the apparatus becomes complex.
Further, the electrophotographic apparatus according to the prior art has suffered from a disadvantage that the two-dimensional size of the image being copied cannot be freely chosen. For example, in such an electrophotographic apparatus, where reduction or enlargement is to be effected two-dimensionally, it is effected with the imaging lens system 3 as the magnification changing mechanism. Where an original written on paper of U.S. letter size or legal size is to be copied on copying paper of size A or B, the imaging magnification in the y direction of the original is adjusted by the magnification changing mechanism which is the imaging lens system 3 and the imaging magnification in the x direction of the original is adjusted by the feeding velocity m of the original and the angular velocity M of the light-receiving member 12. As a result, where the ratio of the length to the width of the original differs from the ratio of the length to the width of the copying paper, the electrophotographic apparatus according to the prior art has suffered from a disadvantage that as shown in FIG. 4A of the accompanying drawings, unnecessary space is created in the copying paper or a part of the original fails to be recorded. Accordingly, in order to prevent such unnecessary space from being created in the copying paper, it is necessary to make the imaging lens system 3 into a magnification changing optical system and insert the cylinder lens 14, but again in this case, a disadvantage has arisen that the length of the optical path between the imaging lens system 3 and the light-receiving member 12 is varied by the insertion of the cylinder lens 14 and a clear image cannot be obtained.